1. Field of the Invention
In the production of plasticizer-free films of polyvinyl chloride (PVC) by the calender process, lubricants are required which are good release agents and which provide for safe removal of the hot films from the calender roll. Preferably, the lubricants employed are useful as release agents for both normal, unmodified polyvinyl chloride molding compositions and also for high-impact, modified polyvinyl chloride molding compositions. The releasing effect required presupposes a certain incompatibility between the lubricant and the polyvinyl chloride to enable the lubricant to be concentrated at the surface of the film; this incompatibility ideally should not affect film quality, particularly film light-transmitting properties. Glass-clear articles should be able to be produced, even when relatively large quantities of lubricant are used, as is typically the case in the production of very thin films. In many cases, however, it is not possible optimally to satisfy both requirements. In the interests of the necessary release effect, compromises are often made to the detriment of the transparency of the product.
2. Discussion of Related Art
Known lubricants useful in the production of unplasticized PVC films include montan waxes and substantially neutral mixed esters of aliphatic, cycloaliphatic or aromatic C.sub.2 -C.sub.22 -dicarboxylic acids, aliphatic C.sub.2 -C.sub.6 -polyols and aliphatic C.sub.12 -C.sub.30 -monocarboxylic acids having hydroxyl or acid numbers of from 0 to 6 (German patent application 19 07 768), and also substantially neutral mixed esters of aliphatic diols, aliphatic, cycloaliphatic or aromatic polycarboxylic acids containing from 2 to 6 carboxyl groups and aliphatic monofunctional alcohols containing from 12 to 30 carbon atoms (German patent application 23 06 744). Montan waxes have the disadvantage that, even in small quantities, they cause serious hazing in unmodified polyvinyl chloride films. In modified polyvinyl chloride, montan waxes are generally too readily soluble so that their release effect is unsatisfactory. The known mixed esters described in the art are attended by the disadvantage that, even in small quantities, they cause relatively serious hazing in modified polyvinyl chloride.